Priority is claimed to patent application No. 2001-30084 filed in Rep. of Korea on May 30, 2001, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a post-exposure treatment method of a holographic recording material, and more particularly, to a post-exposure treatment method of a silver halide emulsion layer in the manufacture of a hologram, a hologram manufactured using the post-exposure treatment method, and a holographic optical element (HOE) including the hologram.
2. Description of the Related Art
Holographic optical elements (HOEs) are recorded in dichromated gelatin (DCG) known to have a high efficiency and low noise characteristics. However, DCG suffers a low sensitivity and poor color reproducibility. Therefore, it is not easy to manufacture a full-color hologram or HOE using the DCG.
For this reason, research on photopolymer or other holographic recording materials has been continuously performed. A silver salt-containing silver halide material and a treatment process thereof have become more interesting in recent years.
As a result of efforts made to attain similar or superior properties to the DCG, a new treatment technique called a xe2x80x9csilver halide sensitive gelatin (SHSG) processxe2x80x9d has been established.
Some research institutes reported that this SHSG process provides a 90% efficiency for transmission HOEs. The SHSG process is characterized as leading a low noise and high efficiency. Also, the residue from the SHSG process is pure gelatin, so there is no problem of print-out.
SHSG techniques developed so far have been applied for recording with holographic materials available from Agfa, Kodak, and liford, causing a problem of scattering during recording. No scattering is observed when applied to the DCG or photopolymers.
The recent development of some sorts of ultra-fine grain silver halide emulsion has increased an interest in the SHSG technique. This is because the SHSG technique is expected to provide comparable effects with the DCG when applied to an ultra-fine grain silver halide emulsion. However, there hasn""t been reported yet a SHSG technique capable of effecting similar properties to the DCG or photopolymers.
Briefly, the SHSG technique involves exposing and locally tanning a silver halide emulsion layer. Then, silver salt or silver in the emulsion layer diffuses out due to fixing, so that only pure gelatin remains. In the last step, the remaining gelatin is dehydrogenated using a hydrophilic organic solvent. The dried SHSG hologram includes only gelatin and microvoids of air. Like this, since the internal component of the dried SHSG hologram varies and refractive indexes of the two components differ, that is, the gelatin has a refractive index of 1.5, and the air filling the microvoids has a refractive index of 1.0, the refractive index of the SHSG hologram with respect to incident light varies. The SHSG hologram or a HOE including the SHSG hologram (hereinafter, referred to as an xe2x80x9cSHSG HOExe2x80x9d) operates using the variation of refractive index.
SHSG holograms or SHSG HOEs are categorized into a transmission type or a reflection type according to the transmittance of the hologram at recording or reproduction. It has been known that the reflection type SHSG hologram is more difficult to manufacture than the transmission type SHSG hologram.
A reflection type SHSG hologram having an efficiency of 40-70% has been reported. Also, a reflection type SHSG hologram having an efficiency of 80% was reported in Russia. However, this level of efficiency is impractical. These conventional reflection type SHSG holograms have a problem of the reliability of recording materials or processing reproducibility. This is associated with the fact that the reflection type SHSG hologram or reflection type SHSG HOE has an end structure of multiple layers including a pure gelatin layer and a microvoid layer, which is difficult to be kept intact.
Gelatin or a silver halide emulsion easily swells, collapses, or shrinks during processing. Therefore, it is difficult to keep a fringe that is an interference pattern formed during recording. Thus, a SHSG hologram with excellent quality cannot be manufactured using the gelatin or silver halide emulsion.
An SHSG process using a red sensitive BB-640 emulsion (ultra-fine grain silver halide emulsion) having a grain size of 25 nm was reported by Blendze and Neipp. The SHSG process provides an improved efficiency above 90%, compared to 40% for an Agfa""s product and 85% for a simple BB640 emulsion.
Bledze reported an efficiency of 90% using a red-sensitive PFG-01 emulsion. Usanov succeeded in manufacturing a reflection type hologram through reversal solvent bleaching with an efficiency of 80% for each wavelength of the R, G, B colors. However, his disclosure was not fully described, and the efficiency is not high enough for practical use.
Holographic recording materials that have been developed or reported as having been developed so far, such as DCG or photopolymer, fail to fully meet the requirement of characteristics. The DCG has excellent efficiency, signal-to-noise ratio (S/N), and long-term reliability, but very low photosensitivity and spectral sensitivity. Therefore, the DCG has limited applications. The photopolymer is excellent in most characteristics, but is slightly unstable and difficult to handle. Up to now, no photopolymer has been produced on an industrial scale.
Common silver halide emulsions have been found to be inferior to the DCG or photopolymer in all of the characteristics. There has not been reported any SHSG process capable of providing a comparable effect to the DCG or photopolymer using ultra-fine grain silver halide emulsion.
To solve the above-described problems, it is an object of the present invention to provide a post-exposure treatment method of a silver halide emulsion layer, capable of providing excellent spectral sensitivity, energy sensitivity, efficiency, signal-to-noise ratio, and long-term reliability as well as the advantages of conventional silver halide, dichromated gelatin (DCT), and photopolymers.
It is a second object of the present invention to provide a hologram manufactured using the post-exposure treatment method and a holographic optical element (HOE) employing the hologram.
To achieve the first object of the present invention, there is provided a post-exposure treatment method of a silver halide emulsion layer in the manufacture of a hologram, the method comprising: pre-hardening the silver halide emulsion layer after exposure; developing the pre-hardened silver halide emulsion layer using a high-contrast developer solution; bleaching the developed silver halide emulsion layer; hardening the bleached silver halide emulsion layer; drying the hardened silver halide emulsion layer; surface-hardening the dried silver halide emulsion layer; fixing the hardened silver halide emulsion layer; treating the fixed silver halide emulsion layer using warm water; and drying the silver halide emulsion layer which has been treated using warm water.
In pre-hardening the silver halide emulsion layer, preferably, a mixture of an organic solvent including an aldehyde group, potassium bromide, sodium carbonate, and deionized water in a predetermined ratio is used.
In bleaching the developed silver halide emulsion layer, preferably, a hardening agent of 1-8% for cross-linking gelatin in the silver halide emulsion layer and a rehalogenate-bleaching agent containing a basic substance of 0-5% for the adjustment of pH are used.
In hardening the bleached silver halide emulsion layer, the bleached silver halide emulsion layer can be thermally treated to harden gelatin in the bleached silver halide emulsion layer. Preferably, the bleached silver halide emulsion layer is left in warm water, a high-temperature and high-humidity atmosphere, or a microwave oven for a predetermined period of time to facilitate the cross-linking of the gelatin.
Preferably, before bleaching the developed silver halide emulsion layer, the post-exposure treatment method according to the present further comprises treating the developed silver halide emulsion layer in a stop bath, for example, using acetic acid for 30-120 seconds.
In the post-exposure treatment method according to the present invention, drying the hardened silver halide emulsion layer can comprise: treating the hardened silver halide emulsion layer using a dilution of an organic solvent with water, preferably in a 50:50 ratio, for a predetermined period of time, preferably 2-3 minutes and then 100% of the organic solution for a predetermined period of time, preferably 2-3 minutes, and drying the resultant structure; drying the resultant structure in an oven at a temperature, preferably of 45xc2x0 C., for a predetermined period of time, preferably 5 minutes. The organic solvent can be ethanol or IMS (Industrial Methylated Spirit).
In surface-hardening the dried silver halide emulsion layer, preferably, the surface of the dried silver halide emulsion layer is thermally treated after surface coating of the dried silver halide emulsion layer using one of an aldehyde-containing solution and a metol- or quinol-containing organic solvent for a predetermined period of time, or is thermally treated within a sealed container under the atmosphere of a vapor of the aldehyde-containing solution or metol- or quinol-containing solution for a predetermined period of time.
Alternatively, in surface-hardening the dried silver halide emulsion layer, the surface of the dried silver halide emulsion layer can be coated with one of an aldehyde-containing solution and a metol- or quinol-containing organic solvent and then thermally treated using a microwave oven for a predetermined period of time.
In fixing the hardened silver halide emulsion layer, preferably, a 2-10% dilution of a fixing solution is used to form microvoids. Preferably, the fixing solution comprises one selected from the group consisting of ammonium thiosulfate, sodium thiosulfate, ammonium thiocyanate, and a 1:2-2:20 dilution of ILFORD rapid, and an anti-swelling agent for suppressing collapsing of the microvoids and swelling of gelatine.
In treating the fixed silver halide emulsion layer using warm water, preferably, the fixed silver halide emulsion layer is treated using warm water of 30-80xc2x0 C. for 1-10 minutes.
Preferably, drying the silver halide emulsion layer that has been treated with warm water in the post-exposure treatment method according to the present invention comprises: sequentially treating the silver halide emulsion layer which has been treated with warm water using a mixed organic solvent, pure organic solvent, and high-temperature organic solvent, preferably, not less then 70xc2x0 C.; and slowly exposing the treated silver halide emulsion layer to air so that water remaining in the microvoids and gelatine of the silver halide emulsion layer is displaced by air. In this case, preferably, the mixed organic solvent comprises 40-80% of an organic solvent and 60-20% of water. The organic solvent can be isoproanol.
When water and the organic solvent remain in the microvoids after the drying, preferably, the silver halide emulsion layer that has been exposed to air is dried in an oven, preferably, not less than 40xc2x0 C., or in a vacuum oven for a predetermined period of time, to completely remove water and the organic solvent remaining in the microvoids.
Preferably, the post-exposure treatment method according to the present invention further comprises, after drying the silver halide emulsion layer which has been treated with warm water, coating the surface of exposed gelatine with solvent-free epoxy or UV curable cement, or sealing the surface of exposed gelatine with glass, polyester, acrylic, or triacetate film.
The second object of the present invention is achieved by transmission and reflection holograms for both monochromic and color display, transmission and reflection holographic optical elements, a high-efficiency full-color hologram grating element, monochromic and color hologram reflectors, an edge-lit hologram and an HOE having the edge-lit hologram, an evanescent wave hologram and an HOE having the evanescent wave hologram, monochromic and color hologram diffusers, monochromic and color hologram screens, a color filtering device, a dichroic mirror and filter, a hologram using IR or near IR and a holographic IR optical element having the hologram, and a holographic IR optical element operating using light having a wavelength shifted from the wavelength of recording light, all of which are manufactured using the post-exposure treatment method described above.
The second object of the present invention is achieved by optical devices including an active optical switching device, an active hologram or HOE, a compact laser, and a light amplifier, which comprise a hologram manufactured using the post-exposure treatment method described above so that microvoids of the hologram are filled with a material having a different refractive index from gelatin, a bandgap material, or a material working by potential difference, such as liquid crystals.
As described above, since the post-exposure treatment method according to the present invention is based on the conventional silver halide emulsion layer, the characteristics of dichromated gelatin (DCG) and photopolymers can be provided with better spectral sensitivity, energy sensitivity, efficiency, signal-to-noise ratio, and long-term reliability than the conventional holographic recording materials. In addition, by adjusting the temperature of treatment, the bandwidth and reproduction wavelength can be varied. The post-exposure treatment method of a silver halide emulsion layer according to the present invention is applied to manufacture a full-color hologram and HOE, other optical elements, and displays with improved efficiency, signal-to-noise ratio, bandwidth, and long-term reliability, compared to conventional holograms and HOEs.